Tamilnadu Board Class 12 Physics Practical - Byju's

Higher Secondary Second Year

PHYSICS

PRACTICAL

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LIST OF EXPERIMENTS

1.Determination of the specific resistance of the material of the given coil using metre bridge.

2.Determination of the value of the horizontal component of the Earth's magnetic field using tangent galvanometer.

3.Determination of the magnetic field at a point on the axis of a circular coil.

4.Determination of the refractive index of the material of the prism by finding angle of prism and angle of minimum deviation using spectrometer.

5.Determination of the wavelength of a composite light by normal incidence method using diffraction grating and spectrometer (The number of lines per metre length of the grating is given).

6.Investigation of the voltage-current (V-I) characteristics of PN junction diode.

7.Investigation of the voltage-current (V-I) characteristics of Zener diode.

8.Investigation of the static characteristics of a NPN Junction transistor in common emitter configuration.

9.Verification of the truth table of the basic logic gates using integrated circuits.

10.Verification of De Morgan's theorems using integrated circuits.

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1. SPECIFIC RESISTANCE OF THE MATERIAL OF THE COIL USING METRE BRIDGE

AIMTo determine the specific resistance of the material of the given coil using metre bridge.

APPARATUS REQUIRED Meter bridge, galvanometer, key, resistance box, connecting wires, Lechlanche cell, jockey and high resistance.

FORMULA

= X r2 (m) L

where, X Resistance of the given coil () R Known resistance ()

L Length of the coil (m)

r Radius of the wire (m)

CIRCUIT DIAGRAM

X

R

D

G1

G2

G

0 10 20 30 40 50 60 70 80 90 100

A

J

HR

B

l

(100 - l)

+?

()

Lechlanche cell

K

PROCEDURE

? A resistance box R is connected in the left gap and the unknown resistance X in the right gap. ? A Lechlanche cell is connected across the wire of length 1 m through a key. ?Asensitive galvanometer G is connected between the central strip and the jockey through a

high resistance (HR).

? With a suitable resistance included in the resistance box, the circuit is switched on. ?To check the circuit connections, the jockey is pressed near one end of the wire, say A.

The galvanometer will show deflection in one direction. When the jockey is pressed near the other end of the wire B, the galvanometer will show deflection in the opposite directions. This ensures that the circuit connections are correct.

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?By moving the jockey over the wire, the point on the wire at which the galvanometer shows

null deflection i.e., balancing point J is found.

? The balancing length AJ = l is noted.

?

R (100 - l )

The unknown resistance X1 is found using the formula X1 =

l

.

? The experiment is repeated for different values of R.

?The same procedure is repeated after interchanging R and X.

?The

unknown

resistance

X2

is

found

using

the

formula

X2

=

Rl .

(100 - l )

?The experiment is repeated for same values of R as before.

?The resistance of the given coil is found from the mean value of X1 and X2. ? The radius of the wire r is found using screw gauge.

? The length of the coil L is measured using meter scale.

?From the values of X, r and L, the specific resistance of the material of the wire is determined.

OBSERVATION length of the coil L = ____________________________________ cm.

Table 1 To find the resistance of the given coil

S.No. 1

Resistance R ()

Before interchanging

Balancing

length l (cm)

X1

=

R (100 - l )

() l

After interchanging

Balancing length l

(cm)

X2 = ()

Rl

(100 -

l

)

Mean X = X1 + X2

2

()

2

3

Mean resistance, X = -----------

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Table 2 To find the radius of the wire

Zero error

=

Zero correction =

Sl.No.

PSR (mm)

HSC (div.)

1 2 3 4 5 6

Total Reading = PSR + (HSC ? LC)

(mm)

LC = 0.01 mm Corrected Reading

= TR ? ZC (mm)

Mean diameter 2r = . . . . . . . . . . . cm Radius of the wire r = . . . . . . . . . . . cm

r= ........... m

CALCULATION (i) = X r2 =

L

RESULT The specific resistance of the material of the given coil = _____________________(m)

Note:

i)To check the circuit connections:

The meter bridge wire is touched near one end (say, end A) with jockey, galvanometer shows a deflection in any one direction. Now the other end (say, end B) is touched. If the galvanometer shows a deflection in the opposite direction, then the circuit connections are correct.

ii)The usage of high resistance (HR):

The galvanometer is a very sensitive device. If any high current flows through the galvanometer, its coil gets damaged. Therefore in order to protect the galvanometer, a high resistance (HR) is used. When HR is connected in series with the galvanometer, the current through it is reduced so that the galvanometer is protected. But the balancing length is not accurate.

iii) To find the accurate balancing length:

The HR is first included in the circuit (that is, the plug key in HR is removed), the approximate balancing length is found. Now HR is excluded in the circuit (that is, the plug key in HR is closed), then the accurate balancing length is found.

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2. HORIZONTAL COMPONENT OF EARTH'S MAGNETIC FIELD USING TANGENT GALVANOMETER

AIM To determine the horizontal component of the Earth's magnetic field using tangent galvanometer.

APPARATUS REQUIRED Tangent galvanometer (TG), commutator, battery, rheostat, ammeter, key and connecting wires.

FORMULA

BH

=

?0n 2r

k

(Tesla)

k

=

I tan

(A)

where, BH Horizontal component of the Earth's magnetic field (T)

?0 Permeability of free space (4 ? 10-7 H m-1)

n Number of turns of TG in the circuit (No unit)

k Reduction factor of TG (A)

r Radius of the coil (m)

CIRCUIT DIAGRAM

Clrcular coil

Pointer Terminals

Compass box Leveling screw

Figure (a) Tangent Galvanometer Figure (b) Number of turns

k

()

Bt

+?

C

TG

+A ?

Rh

(c) Circuit diagram

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PROCEDURE

? T he preliminary adjustments are carried out as follows. a.The leveling screws at the base of TG are adjusted so that the circular turn table is horizontal

and the plane of the circular coil is vertical.

b.The circular coil is rotated so that its plane is in the magnetic meridian i.e., along the north-

south direction.

c.The compass box alone is rotated till the aluminium pointer reads 0? - 0?. ? T he connections are made as shown in Figure (c).

? The number of turns n is selected and the circuit is switched on. ? The range of current through TG is chosen in such a way that the deflection of the aluminium

pointer lies between 30? - 60?. ? A suitable current is allowed to pass through the circuit, the deflections 1 and 2 are noted from

two ends of the aluminium pointer. ? Now the direction of current is reversed using commutator C, the deflections 3 and 4 in the

opposite direction are noted. ? The mean value of 1, 2, 3 and 4 is calculated and tabulated. ? The reduction factor k is calculated for each case and it is found that k is a constant. ? The experiment is repeated for various values of current and the readings are noted and tabulated. ? The radius of the circular coil is found by measuring the circumference of the coil using a thread

around the coil. ? From the values of r, n and k, the horizontal component of Earth's magnetic field is determined.

Commutator:

It is a kind of switch employed in electrical circuits, electric motors and electric generators. It is used to reverse the direction of current in the circuit.

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OBSERVATION Number of turns of the coil n = Circumference of the coil (2r) = Radius of the coil r =

S.No Current I

(A) 1 2 3 4

Deflection in TG (degree)

1

2

3

4

Mean (degree)

Mean

CALCULATION

BH

=

?0n 2r

k

=

RESULT The horizontal component of Earth's magnetic field is found to be ________

k

=

I tan

Note:

i)The magnetic materials and magnets present in the vicinity of TG should be removed. ii)The readings from the ends of the aluminium pointer should be taken without parallax

error.

iii)T he deflections of TG is restricted between 30? and 60?. It is because, the TG is most sensi

tive for deflection around 45? and is least sensitive around 0? and 90?. We know that I = k tan

or dI =k sec2 d d = sin2 dI 2I

For given current, sensitivity d maximum for sin 2 = 1 or = 45? dI

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